Conventional two-way time division multiplex (TDM) radio architectures have several interstitial radio frequency (RF) filters in both the transmitter and receiver sections of the radio. In FIG. 1, there is shown a prior art TDM radio 100. Radio 100, includes a bandpass filter (BPF) 102, located in the receiver section of radio 100. The input terminal of filter 102 is electrically coupled to a conventional antenna switch 104. The output terminal of filter 102 is in turn coupled to a low noise amplifier (LNA) 106 used for amplifying the received radio frequency signal. The low noise amplifier 106 is followed by another bandpass filter 108 in order to further filter the received signal. The output of filter 108 is coupled to mixer 110 where the received signal is mixed with the first injection signal 120 coming from synthesizer 122. The resulting IF signal is then passed through another bandpass filter 124 prior to the filtered IF signal being sent to the receiver back-end circuitry 128 in order to gather the desired receiver component coming from mixer 110.
The transmitter section of radio 100 includes a second LO (local oscillator) signal 126 which is produced by the transmitter front-end (not shown) and which is mixed by mixer 130 with the 1st injection signal 120. The output signal of mixer 130 is then sent to a band pass filter 112, which is typically located at the input to the transmitter power amplifier 114, in order to gather the desired transmitter component coming from mixer 130. Finally, a low pass filter 116, is coupled to the output of the power amplifier 114 in order to further filter the RF signal prior to the RF signal being sent to antenna 118.
Two consecutive radio blocks (e.g., LNA 106, T/R switch 104, etc.) cannot be easily integrated if they have an "off-chip" filter between them (filters 102, 108, 112 and 116). This is because doing so would cause the "off-chip" filter to lose much of its selectivity characteristics due to the stray electric and inductive coupling created by the large physical size of the interconnecting wires of the "off-chip" filter, as compared to the size of the integrated section (IC) to which the filter is being coupled. Trying to provide an "off-chip" filter between integrated blocks would defeat the purpose of integrating any portion of the R.F. section at all. Thus, contemporary Time Division Multiplexed (TDM) radios have the R.F. sections of the radios comprised of many lumped or small scale integrated blocks with filters coupled between the blocks.
A need thus exists for a radio architecture which can be integrated more easily. The improved integration can provide for substantial size and cost reductions to the final radio product.